The invention relates to an electric machine comprising a stator and a rotor separated by an air gap, with
(a) the rotor being composed with permanent magnets magnetized substantially in a circumferential direction, and with one magnetic flux conducting piece assembly including at least one magnetic flux conducting piece between two adjacent permanent magnets;
(b) the permanent magnetsxe2x80x94when looking at the overall geometryxe2x80x94each having an increasing circumferential width from the head portion on the side of the air gap to the foot portion;
(c) and the conducting piece assemblies between two adjacent permanent magnetsxe2x80x94when looking at the overall geometryxe2x80x94each having a decreasing circumferential width from the head portion on the side of the air gap to the foot portion.
The electric machine may be, in particular, an electric motor or a current generator. The invention relates, in particular, to electric machines in which the air gap has a substantially cylindrical configuration.
In the electric machines of the type indicated at the outset, a considerable magnetic force acts on each of the magnetic flux conducting pieces in the direction towards the air gap. When the machine is formed with an internal rotor, the centrifugal force acting on the magnetic flux conducting piece assembly is superimposed on the force of attraction during operation of the machine so as to increase the same. When the machine is formed with an external rotor, the centrifugal force now acting on the magnetic flux conducting piece assemblies in the opposite direction is superimposed on the magnetic force of attraction during operation of the machine. The overall geometry of the conducting piece assemblies with decreasing circumferential width from the head portion on the side of the air gap to the foot portion further aggravates safe locating of the conducting piece assemblies in the rotor.
The problem to be solved by the invention is to make available electric machines of the type indicated at the outset, in which the conducting piece assemblies are held on the rotor in a constructionally simple, but nevertheless extremely reliable manner.
According to a first solution of this problem, the machine according to the invention is characterized in
(d) that the conducting pieces at the foot end each have a widened portion in circumferential direction, having at least one shoulder through which they are supported on an adjacent permanent magnet against displacement in the direction towards the air gap.
Due to the provision of the widened portion at the foot end of the particular conducting piece, the widened portion indeed is not located in an optimum region under the aspect of mechanical strength, said region being narrower in circumferential direction than at a location further towards the head end. On the other hand, the widened portion is situated in a region where the relatively lowest impairment results for the configuration that is advantageous in terms of magnetic flux passage.
It is pointed out that the at least one shoulder need not necessarily extend substantially in tangential direction of the rotor (although this constitutes a preferred embodiment), but may also extend obliquely with respect to the tangential direction, but parallel to the rotor axis.
According to a second solution of the above-indicated problem according to the invention the machine is characterized in
(d) that the conducting pieces each have at least one shoulder through which they are supported on a supporting member against displacement in the direction towards the air gap, the supporting member being constituted by the rotor or attached to the rotor.
In this solution according to the invention, the at least one shoulder thus is no longer provided necessarily at the foot end of the respective conducting piece, but may be provided at any location of the radial extension of the conducting piece.
With numerous embodiments of the invention, the respective conducting piece assembly comprises only one conducting piece between two adjacent permanent magnets. Especially in this case, it is, as a rule, practical and favorable to provide the respective conducting piece on both sides with a shoulder, though it is alternatively possible, as well, to utilize a shoulder on only one side of the conducting piece.
According to another, preferred development of the invention the conducting piece assemblies consist of two conducting pieces each, having a shoulder on one side or on both sides. Conducting piece assemblies with more than two conducting pieces are possible as well.
Preferably, two conducting pieces each of adjacent conducting piece assemblies can be connected to each other via the permanent magnet disposed therebetween. This results in a U-shaped conducting piece configuration enclosing the interposed permanent magnet and thus being supported on the latter.
It is preferred, furthermore, that a pocket be formed between the two conducting pieces of the respective conducting piece assembly, in which a supporting member is disposed. With this configuration, a portion of the conducting pieces that is not adjacent the permanent magnets thus is employed for fixing them to the rotor. According to a further development it is advantageous to connect two supporting members of two adjacent conducting piece assemblies so as to form a common supporting frame. This renders the construction somewhat more complex indeed, but provides the possibility of a particularly stable fixation of the supporting members on the rotor.
The expression xe2x80x9cat least one shoulderxe2x80x9d as used repeatedly hereinbefore covers on the one hand the possibilities that a shoulder is provided only on one circumferential end or that a shoulder is provided on both circumferential ends. On the other hand, this also covers the possibilities that two or even more shoulders are provided radially behind each other at the corresponding location (e.g. a so-called fir-tree foot), or only one shoulder without radially spaced neighbouring shoulder (which is the most frequent design).
According to a third solution of the problem mentioned, the machine according to the invention is characterized in
(d) that the conducting piece assemblies each include one conducting piece retained on the rotor by means of an axially extending bolt.
This construction is particularly simple with respect to the manufacture of the conducting piece assemblies, since no external shoulders, pockets or the like have to be produced, but rather the bolt can be passed e.g. through a drilled or punched hole in the conducting piece assembly. Provision of a bolt in the foot end region of the conducting piece normally is preferred since there the magnetic flux passage is impaired least.
According to a fourth preferred solution of the problem mentioned, the machine according to the invention is characterized in
(d) that the rotor comprises a plurality of thin round plates spaced apart in the direction of the rotor axis, and in that the conducting piece assemblies and/or the permanent magnets are divided into axial partial lengths that are attached to the round plates.
The fourth solution realizes the conception that the forces arising at the conducting piece assemblies and/or the permanent magnets (in particular the forces of magnetic attraction in radial direction and the centrifugal forces) are divided to partial lengths of the conducting piece assemblies and/or of the permanent magnets, so as to dissipate them so to speak in shares. As will be pointed out in more detail hereinafter, there is a number of preferred possibilities of providing the connections between the partial lengths and the round plates, in particular by adhering and clamping them to each other. It is to be understood that the round plates preferably are fixed in the remainder of the rotor structure, e.g. also to the bandage to be described still in more detail hereinafter, and to that location dissipate the holding forces for holding the partial lengths of the conducting piece assemblies and/or the permanent magnets.
It is preferred to use non-ferromagnetic material for the round plates. It is particularly preferred when the material in addition thereto is not electrically conducting.
It is expressly pointed out that the four solutions disclosed, if desired also inclusive of one or several associated developments, can be combined with each other in twos, threes or also fours. Thus, it is possible e.g. to provide the fourth solution (attachment of axial partial lengths to round plates which in turn are part of the rotor or are attached thereto) along with the first solution (shoulder support of the conducting pieces on adjacent permanent magnets), so as to provide, so to speak, a second safety line.
The round plates preferably have essentially the same radial dimension as the conducting piece arrangements and the permanent magnets, or preferably have a radially projecting length on the side facing away from the air gap. In the first case, manufacture can also proceed such that a radially projecting length of the round plates radially inside and/or radially outside is provided first, which then is removed e.g. by turning. The alternative of maintaining a radially projecting length of the round plates on the side facing away from the air gap provides the advantage that mechanical stability of the rotor is increased, that longer rotors in axial direction can be built and that higher speeds of the rotor are permissible.
It is preferred according to a further development to clamp together the xe2x80x9cpackagexe2x80x9d of round plates and partial lengths of the conducting piece assemblies and/or of the permanent magnets by a plurality of circumferentially distributed, axially extending bolts. The bolts can extend through the afore-mentioned radially projecting length of the round plates. The material (permanent magnets, conducting piece assemblies) conducting the magnetic flux then is not reduced in its cross-section. However, it is also possible to provide edge recesses in the conducting piece assemblies and/or the permanent magnets and to have the bolts pass through the round plates and the recesses there, so that no additional space is required for the bolts in radial direction. Finally, it is possible to have the bolts pass through the holes in the round plates and through holes in the conducting piece assemblies and/or the permanent magnets.
The partial lengths of the conducting piece assemblies and/or permanent magnets preferably have recesses or elevations which, for positive engagement, engage with corresponding elevations and recesses in the round plates. In this case, holding together of the xe2x80x9cpackagexe2x80x9d of round plates and conducting piece arrangements and permanent magnets can take place with low clamping force since it is not necessary to rely (solely) on the holding effect by the frictional forces generated by such clamping together.
It is in general a great advantage in particular of the third and fourth solutions that a band or bandage to be described hereinafter is not cogently necessary (but may be present if desired). It is thus possible to avoid the additional thickness required for the bandage, and the machine can be built with smaller housing diameter or larger bore diameter. The structure without a bandage, furthermore, provides the prerequisite that two-sided machines, i.e. a stator radially inside the rotor and an additional stator radially outside the rotor, can be built without a problem.
The following preferred developments can be realized with all four solutions:
The conducting piece assemblies preferably are each symmetrical with respect to a radial plane containing the rotor axis. This often entails manufacturing advantages, but also advantages with respect to the more perfect distribution of the magnetic flux in the particular conducting piece assembly.
In a further development of the invention, it is preferred to form the conducting piece assemblies each as stacked sheet metal assembly, i.e. composed of stacked individual sheet metal plates each located in a plane perpendicularly to the rotor axis. Another favorable alternative is the manufacture of plastics-bound iron particles. However, the conducting piece assemblies need not necessarily be formed as stacked sheet metal assemblies or as stacked metal sheets that are as thin as the winding cores of the stator, since they are not permanently subjected to magnetization reversals.
The rotor preferably is an external rotor, with the permanent magnets and the conducting piece assemblies being mounted on the inside of an annular bandage, preferably of fiber-reinforced plastics material. The outer bandage is perfectly suited to take up the centrifugal forces acting on the permanent magnets and the conducting piece assemblies. However, it may also serve for attachment of the conducting piece assemblies to the rotor, as will be elucidated in more detail by some of the embodiments.
Around the outside of the bandage there may be provided a metallic layer for taking up residual magnetic flux, so that no eddy currents will be induced in a possibly provided outer metal housing of the machine.
When the metallic, layer is provided of ferromagnetic and electrically conducting material, the alternating flows towards the outside are efficiently shielded in the rotor area. It is particularly preferred to use stacked or laminated sheet metal material here, in order to reduce the losses associated with the shielding effect, i.e. the eddy currents. The layer in this respect is formed most suitably by round plates of stamped sheet metal which are stacked in axial direction. Depending on the strength of the metallic layer, it may be sufficient to design the annular bandage just as an isolating layer between permanent magnets and conducting piece assemblies on the one hand and the metallic layer on the other hand, i.e. it may be extremely thin. In the case of a design of such an insulating layer for taking up no considerable loads, the metallic layer in addition is given the function of a load-receiving bandage.
The induction of eddy currents in the outer metal housing of the machine may be prevented in equivalent manner by a laminated metallic sheet metal layer fixedly attached to the inside of the machine housing. In this respect, the same considerations apply as mentioned hereinbefore, however, the alternating flows caused by rotation need to be shielded in addition.
In a preferred development of the invention, the rotor at least on one side axially beside the permanent magnets and the conducting piece assemblies, is provided with a portion serving to mount the permanent magnets and/or the conducting pieces and/or the supporting members and/or the bolts. For, it is sometimes more expedient under constructional aspects not to change to a greater rotor diameter for attaching the components mentioned to the rotor, but to make use of the aforementioned, quasi axially juxtaposed portions.
It is frequently advantageous to provide an adhesive bond between the permanent magnets and the conducting pieces, possibly also between the several conducting pieces of a conducting piece assembly. The adhesive bonds unite the permanent magnets and the conducting pieces of the rotor so that these equal an integral whole. There are xe2x80x9csoftxe2x80x9d adhesives capable of allowing or taking up certain relative displacements between the two adhered components. On the other hand there are xe2x80x9chardxe2x80x9d adhesives not having this effect. In carrying out the invention, it is also possible to use different adhesives at different locations of the rotor; this will be elucidated in more detail by an embodiment described further below.
At the beginning of the description, the expression xe2x80x9cwhen looking at the overall geometryxe2x80x9d (of the particular permanent magnet or of the particular conducting piece assembly) has been used. This is supposed to point out that the circumferential width does not necessarily have to increase or decrease, respectively, from head portion to foot portion in uniform or monotonous manner. It is dependent on the overall configuration, and e.g. an in total increasing circumferential width indeed may be decreasing over a distance and increase again thereafter. A good example can be seen in the widened portions at the foot end of the conducting pieces according to the invention. Although in case of the conducting piece assembliesxe2x80x94when looking at the overall configuration the circumferential width decreases from the head portion on the side of the air gap to the foot region, the expression can cover a more local widening in circumferential direction at the foot end.
It is pointed out in addition that the machine according to the invention preferably is composed in accordance with the flux concentration principle. The half of the flux exit area of each conducting piece assembly at the air gap is to be smaller than the projected area of one of the two adjacent permanent magnets, with the projected area being located in a radial plane containing the rotor axis. Due to this condition, a greater magnetic flux concentration is present at the air gap than at the magnetic flux-producing permanent magnets.